1. Field
Example embodiments relate, generally, to an NPN-type organic compounds, and organic semiconductor films and electronic devices fabricated using such compounds, for example, to NPN-type low molecular aromatic ring compounds, organic semiconductor films formed from such compounds via a solution-based process for example, spin coating at room temperature, and electronic devices including such organic semiconductor films.
2. Description of the Related Art
Flat display devices, for example, liquid crystal display devices and organic electroluminescent display devices, are typically provided with one or more types of thin film transistors for controlling the operation of the display devices. The basic thin film transistor structure comprises a gate electrode, source/drain electrodes, and a semiconductor layer forming a channel region in which the conductivity can be controlled through the operation of the gate electrode. The p-type or n-type semiconductor layer functions as conductive channel material through which current will flow between the source and drain electrodes when an appropriate voltage level is applied to the gate electrode.
Various low molecular weight organic materials, for example, pentacene, have been investigated for use as organic semiconductor materials. As a result of these investigations, the properties and electrical behavior of various such organic materials have been determined. Pentacene, for example, has been reported to have a charge mobility in the range of 3.2 to 5.0 cm2/V-s or perhaps more, but has also been deemed unsuitable for general fabrication processes as a result of the costs and complexity associated with the formation of such a film over larger areas, the need for expensive vacuum deposition equipment for forming the thin film and the difficulties in forming a fine pattern from the thin film.
On the other hand, certain other polymeric or oligomeric organic semiconductors, while tending to exhibit lower charge mobility levels than other low molecular weight organic materials, for example, pentacene, can provide cost advantages as a result of the relatively simple processing, for example, spin coating, that can be used to form thin films of these materials over relatively large substrate areas. As such an organic semiconductor, a soluble pentacene precursor capable of being annealed at about 120-200° C. and exhibiting a charge mobility of about 0.1 cm2/V-s has been reported. In addition, an oligothiophene precursor, which has charge mobility of 0.03-0.05 cm2/V-s and may be annealed at 180-200° C., was reported.
Further, PNP-type oligothiophenes having an N-type core have been reported as exhibiting a charge mobility of about 0.00001-0.01 cm2/V-s when using bithiazole as a core, or when configured as a thiophene ring and a benzene ring using thiazole as a core.
However, the PNP-type oligothiophenes mentioned above still tend to be considered less suitable for general fabrication processes because they require the use of vacuum deposition processes for forming a thin film and, further, their P-type π-conjugation is discontinuous as a result of the N-type core. Thus, even though the number of thiophene rings is increased, in the on-state the current flows tend to be unduly limited, and in the off-state the leakage levels tend to be difficult to maintain at a sufficiently low level. The observed leakage levels have generally been attributed, at least in part, to the increased oxidation potential associated with the increased number of thiophene rings.